Synthesis of alkenyl substituted cycloalkanes



United States Patent 3,052,737 SYNTHESIS OF ALKENYL SUBSTITUTED CYCLOALKANES Lynn H. Slaugh, Pleasant Hill, Calif., assignor to Shell Oil Company, a corporation of Delaware No Drawing. Filed Dec. 21, 1959, Ser. No. 860,694 2 Claims. (Cl. 260-666) This invention relates to the conversion of alkenyl cycloalkenes to the corresponding alkenyl substituted cycloalkanes. It deals particularly with a new method for producing such materials in unexpectedly high yield.

The reduction of polar compounds is relatively easy to carry out by well established methods. Special processes have been devised also for the selective reduction of the polar radicals of unsaturated polar compounds, such as unsaturated aldehydes and the like, without at the same time affecting the degree of saturation of the olefinic bonds. Corresponding reactions involving the selective reduction of a particular olefinic bond while leaving unaffected the other olefinic bond in the same molecule of a hydrocarbon have not been studied up to the present time.

It is an object of the present invention to provide a process for the preparation of alkenyl substituted cycloalkanes. It is a particular object of the invention to provide a process for the conversion of alkenyl substituted cycloalkenes to the corresponding alkenyl cycloalkanes. It is a special object of the invention to provide a process with the above objectives in view wherein particularly high yields are obtained. Other objects and advantages of the invention will become apparent from the following description of the process and the reactions employed therein.

Now, in accordance with the present invention, a process is provided wherein adducts are formed between an alkenyl-substituted cycloolefinic hydrocarbon and a polycyclic fused ring hydrocarbon containing in the molecule at least 2 meso carbon atoms in a 1-4 relationship to each other and which can act as a diene in a Diels Alder reaction and in which the double bond formed during this reaction is contained in an aromatic ring, hydrogenating the olefinic linkage contained in the cycloolefin ring, and pyrolyzing the resulting product to regenerate the polycyclic fused ring hydrocarbon and an alkenyl substituted cycloalkane.

The process according to this invention is based upon the discovery that selective adduct formation occurs between a more reactive olefinic linkage which is present in the alkenyl radical as compared with the less reactive olefinic linkage present in the cyclo-olefin group. It is possible that such selective formation may take place in diolefins not containing a cycle-olefin radical as a part of the molecule, but such adduct formation results in a mixture containing a substantial proportion of adducts wherein the linkage between the polycyclic fused ring hydrocarbon is with one of the olefinic linkages of the diolefin and also substantial amounts of adducts wherein the linkage is between the fused ring polycyclic hydrocarbon and the other olefinic linkage of the aliphatic diolefin. Hence, the present process has been found to be especially desirable where high yields of a particular product are desired rather than a mixture of products. The alkenyl cycloalkenes include particularly those in which the alkenyl radical contains between 2 and about 3,052,737 Patented Sept. 4, 1962 18 carbon atoms, preferably between 2 and 4 carbon atoms. The alkenyl radicals may be essentially straightchain or may be branched chain in configuration. The cycloalkene radicals are preferably monocycloalkene and lbicycloalkenes and include those having from 5 to 8 carbon atoms each. Other hydrocarbon radicals may be appended to the cycloalkene radical, particularly alkyl radicals having from 1 to 5 carbon atoms each, more particularly 1-3 carbon atoms each.

The following list of species include typical alkenyl cycloalkenes which may be treated in accordance with this invention:

l-vinyl-l-cyclopentene l-vinyl-l-cyclohexene 4-viny1-l-cyclohexene l-propeny1-1-cyclopentene l-allyl-l-cyclohexene l-propeny1-1cyclohexene 1-methyl-4-ethylidene-l-cyclohexene 1,5-dimethyl-3-vinyl-l-cyclohexane l-methyl-Z-isopropenyl-l-cyciopentene l-methyl-3-isopropylidene-l-cyclohexene 1-isobutenyl-1-cyclohexene 2-methyl-3-isopropenyl-l-cyclohexene 3-methyl-4-isopropenyl-l-cyclohexene 1 methyl-4-isopropenyl-l-cyclohexene 5-methyl-3-allyl-l-cyclohexene Vinyl bicycloheptenes, octenes, etc.

The polycyclic fused ring hydrocarbons with which the alkenyl cycloalkenes form adducts in the first step of the present process include especially those having at least 3 rings per molecule as typified by anthracene and must contain at least 2 meso carbon atoms per molecule in a 1-4 relationship to each other. The following species are typical of the polycyclic compounds which may be employed, the preferred species being anthracene. Alkylated derivatives of these polycyclic hydrocarbons may be utilized but the unsubstituted hydrocarbons are preferred.

Anthracene Benz-as-indacene Napthacene 1,2- benzanthracene Pentacene Hexacene l-Cyclopent (a) Anthracene l-Cyclopent (a) Anthracene B-anthrindane Benzonapthacene Dibenzanthracenes i) The formation of the adducts in the first step of the process can be readily carried out by simply heating at least 1 alkenyl cycloalkene with at least one of the conjugated polycyclic hydrocarbons described above. Temperatures of about C. to about 275 C. can be used. However, a temperature between about 200 and 250 C. is preferred in order to secure the high conversions experienced within reasonably short reaction times. It is usually necessary to heat the ingredients together for a time in excess of about 4 hours and usually between about 4 and 16 hours since the hydrocarbons of this particular type do not form adducts as readily with the polycyclic conjugated hydrocarbons as otherwise materials heretofore employed in the formation of adducts of somewhat similar configuration. Pressures in the order of about 50-5000 pounds per square inch are advisable. The reaction may or may not be carried out in the presence of a hydrocarbon solvent which does not take part in the adduct formation. Suitable hydrocarbon solvents include benzene, toluene, parafiins, gasoline or kerosene fractions from about 1 part of the hydrocarbon solvent to about 100 parts or more per part of alkenyl cycloalkene can be employed.

Stoichiometric proportions or an excess of either of the reactants canbe used in forming the adducts but an excess of olefin is preferred. Advantageous ratios of about 1 to 2 moles of one of the reactants per mole of the other reactant are preferred. Itis usually unnecessary to separate the adduct from the reactionmixture in which it is prepared, although it is usually desirable particularly where in excess of one of the reactants has been employed in forming the adduct to remove any un'reacted component before using the adduct in the reduction step of the process. The thus recovered reactant can then be recycled for further adduct formation.

The reduction of the olefinic group of groups of the adduct formed in the first step of the process can be carried out in a number of different ways by reaction with hydrogen. Catalytic hydrogenation can be carried out with the crude mixture from the adduct formation step preferably after removal of unconverted starting reactants but most preferably without removal of the solvent if solvent was used, by suspending a hydrogention catalyst therein or otherwise contacting the mixture with the catalyst and subjecting the whole to the action of hydrogen.

Any of the hydrogenation catalysts known to the art may be used with .varying degrees of effectiveness in the hydrogenation step of the present process. Of those which are especially adapted to use in accordance with the present invention, the catalysts known to the art as Raneys nickel and Adams platinum catalyst are very eflicacious from the standpoints of both cost and efiiciency. Other suitable hydrogenation catalysts are those consisting of or comprising one or more metals, or catalytically active compounds of metals, such as Fe, Co, Cu, Pd, Zr, Ti, Th, V, Pt, Ta, Ag, Mo, Al, and the like. The catalysts can be used with or without inert or catalytically active carriers or supports or activators.

In a preferred case e.g., when Raney nickel is em- .ployed as the hydrogenation catalyst in an amount from about 2% to about of the product to be hydrogenated, the hydrogenation may be effected satisfactorily at temperatures of from about 30 C. to about 150 C., for example from about 50 to 125 C., and under hydrogen pressures of from about 50 toabout 5000 pounds h or more per square inch. When other catalysts are employed, conditionsleadingto an equivalent degree of hydrogenation are preferably employed. Hydrogenation times of the order of about 0.5 to 8 hours are usually sufficient. At the conclusion of the hydrogenation, the catalyst can be separated from the mixture as by filtration, for example, and reused in the process. In some cases a reactivation treatment may be desirable before such reuse of the catalyst. I

Whatever 'method of reduction is employed the resulting products can be decomposed as previously indicated to liberate the desired alkenyl cycloalkane corresponding to the starting alkenyl cycloalkene and to regenerate the polycyclic fused ring hydrocarbon for reuse in the first step of the process. It has been found that pyrolysis of the reduced adduct is one of the most advantageous methods of carrying out such decomposition. Heating of the reducedadduct at temperatures between about 250 C. and 4509C. (preferably 330-400 C.) is usually effective. The pyrolysis is preferably carried out at ordinary pressures, although higher pressures can be used and sub-atmospheric pressures are also sometimes advantageous in promoting prompt removal of the alkenyl cycloalkene. Such removal is advantageous in any cases as a means of preventing undesirable further reaction of the product. As a rule, heating for a period of about 2 to about 60 minutes is suflicient for substantially complete pyrolysis to the desired products.

In a typical preparation the first step was carried out as follows: Anthracene (1.7 moles) and 4-vinylcyclohexene-l (9.2 moles) together with 800 cc. of toluene were heated at about 225 C. for about 16 hours at a pressure of about 150 psi. The product comprised about by weight of a novel compound, namely, the adduct of anthraceneand 4-vinylcyclohexene-1, which is 9,10-di-. hydro-9,l0[cyclohex-3-enyl]ethanoanthracene. In addition to this relatively pure adduct which was a crystalline material, a non-crystalline product was also obtained in about 14.6% yield. This was later found to be a mixture of the adduct together with a dimer of vinyl cyclohexene and other byproducts. This may be pyrolyzed to recover 4-vinylcyclohexene and anthracene.

The same results were obtained in the absence of any solvent, the recovery of adduct being virtually theoretical. Shorter reaction times in the order of about 6 hours could be utilized if temperatures of about 250 C. were employed, if a less pure product can be tolerated and less than complete reaction is acceptable.

The second step of the process, namely, the hydrogenation of the adduct, was carried out by hydrogenation over Raney nickel at a temperature of about C. and 750 pounds per inch pressure in the presence of isopropyl alcohol to obtain an essentially theoretical yield of the hydrogenated adduct, the only point of hydrogenation being the double bond of the cyclohexene ring. Hydrogenation was also carried out on a corresponding sample in the presence of dimethyl ether of diethylene glycol as the medium. In this case, the temperature was about 50 C. and the pressure utilized was about 500 pounds per square inch to obtain about a 93% yield of the hydrogenated adduct.

The pyrolysis of the hydrogenated adduct was easily carried out by simply heating the product from the foregoing step at a temperature in the order of 330 C. to obtain essentially theoretical yields of anthracene and of vinylcyclohexane. The impure, non-crystalline hydrogenated adduct was also pyrolyzed under similar conditions to recover anthracene and impure vinylcyclohexane.

The latter compound, vinylcyclohexane, has been found to be an important monomer for use in the preparation of polymers by the Ziegler process.

I claim as my invention:

1. A process for producing vinylcyclohexane which comprises adducting 4-vinylcyclohexene-1 as dienophile with anthracene as diene in a Diels-Alder reaction at a temperature between about to 275 C., selectively catalytically hydrogenating the cyclohexene ring of the resulting 9,10-dihydro-9,10-(cyclohex-3-enyl) ethanoanthracene with free hydrogen in the presence of a hydrogenation catalyst at a temperature between about 30 C. and about 150 C. under a hydrogen pressure between about 50 and about 5000 pounds per square inch, and pyrolyzing the hydrogenation product at a temperature between about 330 C. and about 400 C. to produce vinylcyclohexane and regenerate anthracene.

2. A process for producing vinylcyclohexane which comprises adducting 4-vinylcyclohexene-1 with anthracene in a liquid hydrocarbon solvent at a temperature between about 200 C. and about 250 C., hydrogenating the cyclohexene ring of the resulting 9,10-dihydro-9,10-[cyclohex-3-enyl] ethano-anthracene by reaction with gaseous hydrogen at a temperature between about 50 C. and about 125 C. under a hydrogen pressure between about 50 and about 5000 pounds per square inch in the presence of a Raney nickel catalyst, and pyrolyzing the hydrogenation product at a temperature between about 330 C 5 6 and about 400 C. to produce vinylcyclohexane and re- 2,673,886 Steadman Mar. 30, 1954 generate anthracene- OTHER REFERENCES References Cited in the file of this patent D y h y Alder in N r M th ds UNITED STATES PATENTS 5 Preparatwe Orgamc Chem1stry, pages 381 to 511 (pages 434, 488 and 494 only needed). Interscience Publishers 2,406,645 Thomas 27, 1946 Inc., New York, NewYork(1948), 

1. A PROCESS FOR PRODUCING VINYLCYCLOHEXANE WHICH COMPRISES ADDUCTING 4-VINYLCYLOHEXENE-1 AS DIENOPHILE WITH ANTHRACENE A DIENE IN A DIELS-ALDER REACTION AT A TEMPERATURE BETWEEN ABOUT 150 TO 275*C., SELECTIVELY CATALYTICALLY HYDROGENATING THE CYCLOHEXENE RING OF THE RESULTING 9,10-DIHYDRO-9,10-(CYCLOHEX-3-ENYL) ETHANOANTHRACENE WITH FREE HYDROGEN IN THE PRESENCE OF A HYDROGENATION CATALYST AT A TEMPERATUE BETWEEN ABOUT 30*C. AND ABOUT 150*C. UNDER A HYDROGEN PRESSURE BETWEEN ABOUT 50 AND ABOUT 5000 POUNDS PER SQUARE INCH, AND PYROLYZING THE HYDROGENATING PRODUCT AT A TEMMPERATURE BETWEEN ABOUT 330*C, AND ABOUT 400*C. TO PRODUCE VINYLCHCLOHEXANE AND REGENERATE ANTHRACENE. 